The present invention is related to medical devices, and more particularly to medical devices for controlled infusion of fluid into a patient during a medical procedure.
Controlled fluid infusion is crucial in many medical procedures. In some procedures, fluid is used as a distending medium, inflating a body cavity to provide space for surgical instruments and to gain access to a target site in the body cavity. In other procedures, fluid infusion is used to flush out impurities or tissue debris from the patient which may impair visualization and operating efficiency. During the course of such procedures, large volumes of distention fluid such as saline may be circulated in and out of the patient. Unfortunately, poorly controlled infusion of such volumes of fluid can create electrolyte imbalance, water intoxication, or excessive fluid pressures that may be dangerous or even fatal to the patient.
The danger posed by inaccurate fluid infusion, specifically poor fluid pressure control, is particularly relevant to many endoscopic procedures. As an example, hysteroscopic endometrial resection and transurethral resection procedures circulate fluid in and out of the uterus and the bladder, respectively, to provide distension and to remove debris. These body cavities are, however, pressure sensitive environments. Introducing too much fluid too quickly could push distention fluid into the circulatory system of the patient, or worse, rupture these body cavities and cause major internal trauma. Insufficient fluid flow, on the other hand, could cause the body cavity to collapse, reducing the amount of space available for surgery and impairing visibility of the active end of any surgical instruments in the cavity. Hence it is desirable that a user or surgeon be able to accurately control fluid infusion so that the pressure within a body cavity is near an optimal level.
Conventionally, fluid has been infused into a patient by hanging a fluid bag or bottle above the patient and relying on gravity to infuse fluid into the patient. Common practice today eliminates the reliance solely on gravity by using fluid pumps to infuse fluid into the body cavity through a fluid inlet and/or to suction fluid out through a fluid outlet.
Unfortunately, these conventional infusion systems are unable to adequately regulate fluid pressure in a body cavity when there is dynamic fluid flow. Conventional systems typically have pressure controllers that only measure pressure outside of the body cavity, typically using only a single pressure sensor. Although such conventional systems may be able to control body cavity pressure when the fluid is static, once fluid flow starts, the actual pressure inside the cavity may be significantly different from pressure measurements made outside the cavity. Dynamic fluid flow exacerbates pressure drops and measurement errors which occur along the fluid flow path from the fluid source to the point of delivery. Even pressure measurements made closer to the body cavity along the fluid flow path are inaccurate since much of the pressure drop occurs in the instrument or surgical tool delivering fluid into the body cavity. Such discrepancies in pressure may be in the range of 20 to 30 mm Hg and is a significant cause for concern, especially in a rupturable, pressure sensitive environment such as the uterus or the bladder.
Accordingly, it is desirable to have improved fluid infusion methods and systems which are highly accurate, can achieve a desired-fluid pressure in a body cavity, and are stable and responsive. In particular, such a system should overcome the dynamic instability problems associated with prior pump systems to deliver fluid through endoscopic and other instruments into the body cavity, while retaining responsive closed loop control. It would further be desirable if these improved systems were adaptable for use with known endoscopic and other minimally invasive surgical techniques.